In recent years, increased performance of audio-visual apparatus has been pursued. In a television receiving set, a muting circuit is useful as it can eliminate acoustic output while maintaining the image when, for instance, a phone call is received or a child begins to sleep. Conventional technology relating to muting circuits which are used in a television receiver is explained below referring to the drawing.
FIG. 2 is a block diagram of a conventional muting circuit, which involves a mute key input 7, a mute-judging part which achieves either muting or non-muting based upon the mute key input, and an audio output circuit 9 which outputs sound responsive to appropriate signals provided by the mute-judging part 8.
When a muting signal enters the mute key input 7 in the muting circuit, the mute-judging part 8 initiates muting of the acoustic output circuit. The audio output circuit 9, upon receiving appropriate signals from mute-judging part 8, reduces the sound volume to zero decibels, thus achieving muting. If, however, a further signal enters the mute key input 7, the mute judging part 8 generates appropriate signals to conclude muting, and the audio output circuit 9, in turn, restores the previous audio output level. Thus, muting is completed. The conventional structure as mentioned had a shortcoming, however, namely, when an appropriate mute key input signal is applied and the sound is suppressed, any information contained in the audio output (e.g. speech content) is unavailable to the television viewer.